Wireless Power Range Increase Using Parasitic Antennas

ABSTRACT

Wireless power transfer is created using a first antenna that is part of a magnetic resonator, to create a magnetic field in an area of the first antenna. One or more parasitic antennas repeats that power to create local areas where the power is more efficiently received.

This application claims priority from provisional application number60/990,908, filed Nov. 28, 2007, the entire contents of which disclosureis herewith incorporated by reference.

BACKGROUND

Our previous applications have described magneto mechanical systems.Previous applications by Nigel Power LLC have described a wirelesspowering and/or charging system using a transmitter that sends amagnetic signal with a substantially unmodulated carrier. A receiverextracts energy from the radiated field of the transmitter. The energythat is extracted can be rectified and used to power a load or charge abattery.

Our previous applications describe non-radiative transfer of electricalenergy using coupled magnetic resonance. Non-radiative may mean thatboth the receive and transmit antennas are “small” compared to thewavelength, and therefore have a low radiation efficiency with respectto Hertzian waves. High efficiency can be obtained between the transmitresonator and a receive resonator.

SUMMARY

The present application describes extending a range over which thispower transmission can occur using parasitic antennas.

Another aspect describes tuning the parasitic antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings:

FIG. 1 shows a block diagram of wireless power transmission using bothmain and a parasitic transmission antennas;

FIG. 2 shows an antenna around edges of a room;

FIG. 3 shows the antenna at different levels in the room to go arounddoors and windows;

FIG. 4 shows matching circuitry for the parasitic antenna;

FIG. 5 shows a field strength distribution;

FIG. 6 shows a parasitic antenna;

FIG. 7 shows a schematic of switching capacitors;

FIG. 8 shows the field strength;

FIG. 9 shows a variable area antenna;

FIG. 10 shows a coupling loop and antenna;

FIG. 11 shows detuning vs coupling factor;

FIGS. 12A and 12B show transfer efficiency.

DETAILED DESCRIPTION

The classical principle of non-radiative energy transfer is based onFaraday's induction law. A transmitter forms a primary and a receiverforms a secondary separated by a transmission distance. The primaryrepresents the transmit antenna generating an alternating magneticfield. The secondary represents the receive antenna that extractselectrical power from the alternating magnetic field using Faraday'sinduction law.

${{- \mu_{0}}\frac{\partial{H(t)}}{\partial t}} = {\nabla{\times {E(t)}}}$

where ∇×E(t) denotes curl of the electrical field generated by thealternating magnetic field

The inventors recognize, however, that the weak coupling that existsbetween the primary and secondary may be considered as a strayinductance. This stray inductance, in turn, increases the reactance,which itself may hamper the energy transfer between primary andsecondary.

The transfer efficiency of this kind of weakly coupled system can beimproved by using capacitors that are tuned to the precise opposite ofthe reactance of the operating frequency. When a system is tuned in thisway, it becomes a compensated transformer which is resonant at itsoperating frequency. The power transfer efficiency is then only limitedby losses in the primary and secondary. These losses are themselvesdefined by their quality or Q factors.

Compensation of stray inductance may also be considered as part of thesource and load impedance matching in order to maximize the powertransfer. Impedance matching in this way can hence increase the amountof power transfer.

According to a current embodiment, a technique is described for poweringa wirelessly powered device which can be located anywhere within anroom. An embodiment powers the entire room and provides power for areceiver anywhere within the room, independent of the exact position ofthat receiver.

The techniques as disclosed herein operate at a frequency of 135 kHz,the so-called ISM band. However, other techniques may operate at otherfrequencies. For example, other embodiments may operate at a frequencyof 13.56 MHz.

An embodiment uses passive repeaters, referred to herein as parasiticantennas, to extend the range of the wireless power. Power istransferred from a wireless transmitter to all of the parasitic antennasin range. These parasitic antennas form tuned resonators that createareas of maximum power transmission. A wireless power receiver is in therange of the parasitic antenna.

FIG. 1 illustrates a block diagram. A “long-range” room antenna 100 maybe fed with magnetic power by a magnetic frequency generator 105, andamplifier 110. The magnetic generator 105 may produce an output having afrequency which is resonant with the antenna 100. Antenna 100 is formedof an inductive loop 101 as shown, and a separate capacitor 102. Inanother embodiment, the self capacitance of the loop 101 may serve asthe capacitor. The LC constant of the loop and capacitor issubstantially resonant with the frequency created by the generator andamplifier.

This creates magnetic field areas near antenna 100. In an embodiment,the antenna 100 may traverse a perimeter of the room. However, since theantenna 100 produces as much signal inside the loop antenna as it doesoutside the loop, it may be more efficient to place the antenna moretoward the center of a room. Therefore, one embodiment may place theantenna, for example, in the floor, or along edges of a table. Anyreceiver such as 125 can receive power directly from the room antenna100 and can also receive re-radiated power from the antenna 120.

The parasitic antenna 120 receives the magnetic field power from theantenna 100 and reradiates to an area close to 120. The receiver 125 maybe a receiver of magnetic power.

The other receivers shown as 126, 127 can also receive power in the sameway, receiving part or all of their power from the main antenna 100, andpart of the power that is re-radiated by another parasitic antenna 130.Alternately, and in this embodiment, it is shown that the receivers 126and 127 receive power only from the parasitic antenna 130. Yet anotherreceiver 128 is not near a parasitic antenna, and receives magneticallytransmitted power, accordingly, only from the main antenna 100.

The loop antennas may all have the same orientation with respect to themagnetic field, or may each have different orientations with respect tothe magnetic field.

The capability of a receiver antenna to relay power may be mainlydependent on the coupling between the receiver antenna and the roomantenna. This coupling, in turn, is dependent on many factors includingthe area ratio between the receiver antenna and the room antenna. Thereceiver antenna, however, may be limited in size by the size of theportable device that incorporates it. Parasitic antennas can have alarge enough area to allow them to receive and re transmit the power asnecessary.

Another important feature is the quality factor of the antennas. Theparasitic antenna can have higher Q factors, since it can be hidden andof any size.

An embodiment using low-frequency may in general may use more terms ofan inductor then those used at high frequencies. One embodiment may usemultiple turns on the antenna material as part of the antenna 100 andalso the parasitic antenna. One embodiment may use stranded wire, suchas “Litz wire” to compensate for the increased ohmic losses caused bythe increased number of turns. The ohmic losses can be reduced using lowresistance wire.

Litz wire is a special kind of stranded wire, where each single-strandis electrically isolated from the other strand. Litz wire increases theeffective cross-sectional area of the wire, and thereby partiallycompensates for the skin and proximity effect.

More generally, an embodiment may use any material that increases theeffective cross sectional area of a wire used for the antenna withoutincreasing an actual cross sectional area of the wire

The following illustrates differences between conventional wire and Litzwire.

$\begin{matrix}{{D\; C\mspace{14mu} {resistance}\mspace{14mu} {of}\mspace{14mu} a\mspace{14mu} {conventional}\mspace{14mu} {wire}\text{:}\mspace{14mu} R_{D\; C}} = {{\frac{N}{\sigma \cdot b^{2} \cdot \pi} \cdot 2}\; {\pi \cdot r_{A}}}} \\\begin{matrix}{A\; C\mspace{14mu} {resistance}\mspace{14mu} {of}\mspace{14mu} a\mspace{14mu} {conventional}\mspace{14mu} {wire}\text{:}} & {R_{A\; C} = {{\frac{N}{2 \cdot b} \cdot \sqrt{\frac{f \cdot \mu_{0}}{\sigma \cdot \pi}} \cdot 2}\; {\pi \cdot r_{A} \cdot}}} \\\; & {\left( {\alpha + 1} \right)}\end{matrix} \\{{A\; C\mspace{14mu} {resistance}\mspace{14mu} {of}\mspace{14mu} {litz}\mspace{14mu} {wire}\text{:}\mspace{14mu} R_{{A\; C} - {Iks}}} = {{\frac{N}{\sigma \cdot b^{2} \cdot \pi \cdot \xi} \cdot 2}\; {\pi \cdot r_{A}}}} \\{N = {{Number}\mspace{14mu} {of}\mspace{14mu} {{turns}\mspace{11mu}\lbrack 1\rbrack}}} \\{\sigma = {{Electrical}\mspace{14mu} {{conductivity}\mspace{11mu}\left\lbrack {S\text{/}m} \right\rbrack}}} \\{{b = {{Wire}\mspace{14mu} {radius}\mspace{14mu} {\left( {{without}\mspace{14mu} {isolation}} \right)\mspace{11mu}\lbrack m\rbrack}}}\mspace{14mu}} \\{r_{A} = {{Antenna}\mspace{14mu} {circular}\mspace{14mu} {loop}\mspace{14mu} {{radius}\mspace{11mu}\lbrack m\rbrack}}} \\{f = {{Frequency}\mspace{11mu}\left\lbrack {H\; z} \right\rbrack}} \\{\mu_{0} = {{Permeability}\mspace{14mu} {{constant}\mspace{11mu}\left\lbrack {H\text{/}m} \right\rbrack}}} \\{\alpha = {{Proximity}\mspace{14mu} {effect}\mspace{14mu} {{coefficient}\mspace{11mu}\lbrack 1\rbrack}}} \\{\xi = {{Litz}\mspace{14mu} {wire}\mspace{14mu} {packaging}\mspace{14mu} {factor}\mspace{14mu} {\left( {{in}\mspace{14mu} {the}\mspace{14mu} {range}\mspace{14mu} {of}\mspace{14mu} 0.4\text{-}0.6} \right)\mspace{11mu}\lbrack 1\rbrack}}}\end{matrix}$

Based on calculations and simulations, the applicants have found thatthe AC resistance of Litz wire is about 50-80% lower than the ACresistance of a comparable conventional wire that has the same

Inductance of the eventual antenna may be an extremely important factorin the antenna's efficiency of operation. The inductance can beexpressed as

$\begin{matrix}{L_{A} = {\mu_{0} \cdot N^{2} \cdot \frac{A_{A}}{K_{A}}}} \\{A_{A} = {{Area}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {antenna}}} \\{K_{A} = {{antenna}\mspace{14mu} {shape}\mspace{14mu} {factor}}}\end{matrix}$

The factor K_(A) is dependent of the shape of the antenna. For arectangular antenna K_(A) is given by

$K_{\lambda - {rect}} = \frac{A_{A} \cdot \pi}{\begin{matrix}{{{- 2}\left( {w + h} \right)} + {2 \cdot {gswh}} - {{h \cdot \ln}\left( \frac{h + {gswh}}{w} \right)} -} \\{{{w \cdot \ln}\left( \frac{w + {gswh}}{h} \right)} + {h \cdot {\ln \left( \frac{2 \cdot w}{b} \right)}} + {w \cdot {\ln \left( \frac{2 \cdot h}{b} \right)}}}\end{matrix}}$ w = Width  of  the  antenna  [m]h = Height  of  the  antenna  [m]${gswh} = {\sqrt{w^{2} + h^{2}}\mspace{11mu}\lbrack m\rbrack}$

For a circular antenna, K_(A) is given by

$K_{\lambda - {circ}} = \frac{r_{A} \cdot \pi}{\ln \left( {\frac{8 - r_{A}}{b} - 2} \right)}$

The radiation resistance of a loop antenna is given by

$R_{ret} = {320 \cdot \pi^{4} \cdot \left( \frac{A_{A}}{\lambda^{2}} \right)^{2} \cdot N^{2}}$λ = Wavelength  of  operating  frequency  [m]  (2206.8  m  for  135  kHz)

Characteristics of the active antenna can also be calculated using theseformulas. The total resistance of this antenna is formed by the ohmicloss R_(AC), the radiation resistance R_(rad) and the medium lossresistances R_(med). The medium loss resistances models the losses fromthe room in which the antenna is installed. Metallic parts within theroom act like a medium. This medium can be defined according to itscomplex permeability

μ_(med)=μ_(r) ′j·μ _(r)″

μ_(r)′=Real part of relative permeability

-   μ_(r)″=Imaginary part of relative permeability-   Based on this, the medium loss resistance is defined as

R _(med)=2π·ƒ·μ_(r) ″L _(A)

where u″r can be measured, as the relative permeability of the medium,for example as

μ_(med)=1+j·0.0018

This value may change for different rooms, where each room will defineits own media.

FIG. 2 illustrates the room antenna, also called the long-range antenna.This antenna may be long-range by virtue of its size. Larger antennas ofthis type usually have a better capability of coupling magnetic power toa recipient. The embodiment uses a special test room which had anapproximate size of 12 m×5.5 m. The antenna can be mounted at the heightof the table on which the items will be located, but can also be locatedon the floor, where it can be more easily hidden.

One embodiment built the test antennas from RG 213 U coaxial cable. Onlythe outer conductor of this coaxial cable was used. In this embodiment,since the antenna is large, a self capacitance system can be used.

The embodiment of FIG. 2 uses four turns on the ground surrounding thecomplete perimeter of the room. The measured values were

L [μH] R [Ω] C [nF] Q [1] 700 26 2.0 23

Other embodiments may have different values. In this embodiment, Q waslower than expected because of properties of the room.

It was found by experimentation that a single turn antenna in fact inthis medium provided the same performance as a multiple turn antenna.For example, different parameters for different heights produced similarvalues.

L [μH] R [Ω] C [nF] Q [1] 456 7.5 3.1 52 4 turns at 0.4 m  43 0.8 32.346 1 turn at 1.3 m

The antenna can also be removed from the walls by about 1 m, and placedon different heights off the ground. The following shows results forantennas spaced from the wall by 1 m.

L [μH] R [Ω] C [nF] Q [1] 30.9 0.42 45.0 62 1 turn at 0.8 m 31.1 0.444.7 66 1 turn at 2.0 m

Another embodiment, shown in FIG. 3 includes the antenna lifted off theground by some amount, and also lifted at the areas 305, 310 to goaround doors and windows. Measured values for this antenna are asfollows:

L [μH] R [Ω] C [nF] Q [1] 42.34 1.06 33.26 33.7 1 turn at 1.3 m (lifted1.8 m at the windows and 2.1 m above the doors)

The long range antenna 100 may carry a high power. A circuit for theantenna which provides LC values and 50 ohm matching is shown in FIG. 4.According to an embodiment, a special capacitor bank and couplingtransformer is used to the antenna. The values of this device may be:

-   -   C1-C6: 22 nF/900 VAC capacitor Type PHE450 from Revox Rifa    -   P1/P2 Female UHF-connector, designed for RG 213 U cable    -   P3: Female N-connector    -   T1: 2× transformer 1:7. each with 2 ferrite cores of the type        B64290-L659-X830, made of N30 material, secondary winding made        of 3 mm HF litz wire (120×0.1 mm Ø).

In an embodiment, the antenna may carry a power rating of approximately150 W. However, at power levels that are close to this power rating, thecapacitor bank carries a current of 12 amps, total voltage of 400 V.This corresponds to a reactive voltage of 4.8 kVA.

Accordingly, in an embodiment, the capacitor bank is provided on thesecondary side of the transformer. Placing the capacitor bank on theprimary side of the transformer requires the reactive power to passthrough the transformer and to thereby oscillate between the inductanceand capacitance. This would increase the transformer size.

Many rooms include many metal objects, and hence are inherently lossy.The antenna is also intended to have a reasonably large size.Accordingly, the characteristics of this system make it inherentlyimmune from the approaching and moving of people. In essence, this isbecause the area covered by any person is typically small, e.g., lessthan 10% of, the area of the antenna. No tuning of this antenna willtypically be necessary because of these inherent features.

In operation of an embodiment, the fixed installation of the long-rangeantenna creates a magnetic field throughout the entire test roomcreating a transmit power of about 60 W. Actual results as measured areshown in FIG. 5. This three-dimensional graph shows peaks along the walldue to cable loops around doors and at the peak points. The fieldstrength also increases towards the back wall because this wall has lessmetallic part in the test room compared to other walls. The fieldstrength is reduced at the window side due to the metallic frames ofdouble glazed windows.

One embodiment may exploit this effect by placing loops of antennasalong certain walls, e.g., in areas of the room that either need moresignal, or just in general.

Appropriate design of the antenna loop might minimize these hotspots orprovide supplemental antennas to these hotspots. In the central part ofthe room the field strength is often nearly constant.

The power scales according to the square root of the transmit power.Therefore, doubling the transmit power may increase the power density inthe room by √2.

The magnetic field in the room was also measured, and stays withinsafety limits at all points at 60 watts of transmitted power.

FIG. 6 illustrates a parasitic antenna used according to an embodiment.A first embodiment uses a 14 turn loop 600, formed of 120×0.1 mmdiameter high frequency Litz wire. The inductance of the loop isinfluenced by a number of factors including turn-by-turn spacing, wheresmaller spacing between the turns results in a higher inductance andtherefore a higher quality factor.

In the embodiment, the turns are filled with hot glue to secure exactposition. A guide may also be used. The lower limit for the turn to turnspacing is the necessary withstanding voltage of the antenna. Forexample, at 20 W, there may be a 1 K reactive voltage, leading to aturn-to-turn voltage of 75 V. The antenna shown in FIG. 6 includes a 14turn loop 600 forming the inductance and a single turn “coupling loop”606 unconnected to the main loop 600. FIG. 6 shows the antenna builtinto a picture frame.

The capacitance of the parasitic antenna is formed by a bulk capacitance600 and a variable capacitance. The variable capacitance in thisembodiment is formed by a step switch 604 which controls switching of acapacitor bank 603.

FIG. 7 illustrates a capacitor bank that can be used to tune theparasitic antenna The bulk capacitance 602 to may be in parallel withthe tunable capacitance 603 connected via a multiple contacts switch700. The switch position 1 is no extra capacitance, and provides onlythe bulk capacitance. According to an embodiment, this provides aresonant frequency of 137 kHz. More capacitance can be added in parallelwith the capacitor bank by changing to different switch positions.Position 2 provides 90 pf capacitance, for example, and position 3provides 160 pF. 135 kHz resonant frequency is realized at positionthree. Position 6 (330 pf) may tune the frequency to 132 khz.

The antenna may be detuned by nearby metallic objects and the frequencyshift can be corrected by adding more capacitance. The additionalcapacitance may lower the quality factor as the LC ratio of the resonantcircuit is lowered.

Each metallic object inside the generated magnetic field of an antennacompensates a portion of the antenna's total inductance thus results inraising the resonant frequency of the antenna. The antenna does not havea substantial electric field. Accordingly, the presence of dielectricmaterials has very little impact on the antenna. Therefore,low-frequency antennas of the type in an embodiment have resonantfrequencies which shift upward due to detuning effects. A tuningcompensation system according to the present system may accordinglyalways pull down the resonance to provide a non-symmetrical tuningrange.

The parasitic antenna of an embodiment has the followingcharacteristics:

Nominal frequency [kHz] 135 Tuning range (coarse tuning) [kHz] 132-137(in 5 steps) Tuning range (fine tuning) [kHz] +/−0.25 Quality factor 250Inductivity [μH] 260 Bulk capacitance [nF] 5.13 Maximum power capability20 W (approx.) Number of turns 14 Wire Litz wire 120 × 0.1 mm Ø Size 0.7× 0.5 m (average turn size)

Another embodiment may use multiple small capacitors that add togetherto increase the overall capacitance.

Yet another embodiment may use semiconductor switches or relays tochange the capacitance.

Another compensation system is shown in FIG. 8. This provides a shortcircuited loop part 800 within the field of the parasitic antenna 600.This causes a portion of the H field to be compensated, thereby loweringthe inductance of the parasitic antenna. A lower inductance leads to ahigher resonant frequency with a constant capacitance. Accordingly, thistechnique can also be used to tune the resonant frequency of theantenna. The amount of compensation of the resonant frequency isdependent on the ratio between the areas of the main transmit antenna600 and the area of the compensation antenna 800. The area of theshort-circuited loop defines the amount of influence—where a smallerloop has less influence than a larger one.

A conceivable disadvantage of this technique is that the short-circuitedloop lower the overall Q factor of the parasitic antenna.

Another embodiment may implement a short-circuited loop which ismechanically changeable in area. FIG. 9 illustrates an embodiment wherea loop has a variable area by virtue of the ability to move itscharacteristics. The loop in FIG. 9 is a triangular loop with copperplated bars. First bar 902 and second bar 904 are connected together viacenter rotatable couplings such as 903. The bars 902, 904 are alsoconnected together via movable parts 906, 907. The parts 906, 907 can bevaried with reference to one another, and pivoted on the portions 910,911, 912. A spring 915 may assist in folding and unfolding the antenna.In the embodiment, the the main bars 902, 904 are of length X, and thefolding bars 906, 907 are of length X/2. The triangle is deformed bypulling the upper corner of the triangle. However, when the pullingforce gets less, the spring 915 closes the triangle and makes a smallerarea.

Different shapes including rectangles and trapezoids could also be usedfor this purpose.

A receiver antenna is illustrated in FIG. 10. According to thisembodiment, the receiver antenna can be formed of a 70 turn loop of highfrequency litz wire. The receiver antenna 1000 can have turns wound infive layers with 14 turns on each layer. This can form a rectangularprofile where in essence a stack 1002 of wires defines a perimeter thatcan be integrated around the edge of a mobile device. The antennaparameters are shown as:

Nominal Frequency [kHz] 135 Tuning range [kHz] 133-135 Quality factor175 Inductivity [μH] 625 Bulk capacitance [nF] 2.2 Maximum powercapability 2 W (approx.) Number of turns 70 Wire Litz wire 75 × 0.05 mmØ Size 90 × 40 mm (average turn size)

This system can also use a coupling loop which is wholly separate fromthe receiving antenna. The coupling loop can be a three turn loop 1005,for example.

Antenna detuning may occur when coupling between antennas increases andthe antennas begin influencing the inductance of one another and thusinfluence the resonant frequencies. This causes a strong detuning of theantennas. Hence, when a wireless receiver gets too close to theparasitic loop, decoupling can occur. Simulation and measurementproduces the graph of FIG. 11 which shows the impact of coupling factorto the power transfer between two antennas.

An adjustable coupling between antennas may be used to avoid thisdetuning. Multiple taps can be added to the antenna turns and used ascoupling loops. The strength of the coupling can be changed by switchingbetween the taps.

System efficiency defines how the system transfers power to thereceiver. System efficiency is defined by transfer efficiency betweenthe long-range antenna and parasitic loop; transfer efficiency betweenthe long-range antenna and the receiver and transfer efficiency betweenthe long-range antenna to parasitic loop to receiver.

Exemplary results are shown in FIGS. 12A and 12B for the specific testsetup described herein. FIG. 12A shows the single hop transferefficiency, while FIG. 12 B shows the double hop transfer efficiency.

The measurements given above confirm that use of parasitic antennas cancompensate for losses which would otherwise occur due to roomboundaries. The parasitic antennas allow better use of the existingmaterials. Moreover, these can stay within IEEE and NATO definedexposure limit of 125.4 amps per meter at 130 kHz, which can be met atany point in the room at a transmit power of 60 W using a parasiticantenna.

Although only a few embodiments have been disclosed in detail above,other embodiments are possible and the inventors intend these to beencompassed within this specification. The specification describesspecific examples to accomplish˜more general goal that may beaccomplished in another way. This disclosure is intended to beexemplary, and the claims are intended to cover any modification oralternative which might be predictable to a person having ordinary skillin the art. For example, other sizes, materials and connections can beused. Other structures can be used to receive the magnetic field. Ingeneral, an electric field can be used in place of the magnetic field,as the primary coupling mechanism. Other kinds of magnets and othershapes of arrays can be used.

Also, the inventors intend that only those claims which use the-words“means for” are intended to be interpreted under 35 USC 112, sixthparagraph. Moreover, no limitations from the specification are intendedto be read into any claims, unless those limitations are expresslyincluded in the claims.

Where a specific numerical value is mentioned herein, it should beconsidered that the value may be increased or decreased by 20%, whilestill staying within the teachings of the present application, unlesssome different range is specifically mentioned. Where a specifiedlogical sense is used, the opposite logical sense is also intended to beencompassed.

1. A system, comprising: a first system including a transmitting antennaof a first size, transmitting wireless power in a magnetic field; and aparasitic antenna, of a second size smaller than said first size,repeating said wireless power in an area.
 2. A system as in claim 1,wherein said parasitic antenna is a formed of an inductive loop and acapacitance.
 3. A system as in claim 2, wherein said inductive loop isformed of stranded wire with strands that are electrically isolated fromone another.
 4. A system as in claim 2, wherein said inductive loop isformed of a material that increases the effective cross sectional areaof a wire used for the antenna without increasing an actual crosssectional area of the wire.
 5. A system as in claim 1, wherein saidtransmitting antenna surrounds a perimeter of a room.
 6. A system as inclaim 5, wherein said transmitting antenna is at different levels in theroom.
 7. A system as in claim 1, wherein said first system includes afrequency generator, and a matching system, said matching systemincluding a coupling transformer, and a capacitor on a primary side ofsaid transformer.
 8. A system as in claim 2, wherein said parasiticantenna includes a tuning part that is adjustable to change a resonantfrequency of said parasitic antenna.
 9. A system as in claim 8, whereinsaid tuning part includes a variable capacitance.
 10. A system as inclaim 8, wherein said part only adjusts said resonant frequency in adownward direction.
 11. A system as in claim 8, wherein said tuning partincludes a portion that short circuits a portion of said inductive loop.12. A system as in claim 11, wherein said part has a variable size tochange an area of the inductive loop that it short circuits.
 13. Asystem as in claim 12, wherein said part is triangular.
 14. A system asin claim 9, wherein said variable capacitance is a switched capacitance.15. A system, comprising: a parasitic antenna, tuned to receive andrepeat magnetically-generated wireless power in an area of saidparasitic antenna.
 16. A system as in claim 15, wherein said parasiticantenna is a formed of an inductive loop and a capacitance.
 17. A systemas in claim 16, wherein said inductive loop is formed of a material thatincreases the effective cross sectional area of a wire used for theparasitic antenna without increasing an actual cross sectional area ofthe wire.
 18. A system as in claim 17, wherein said inductive loop isformed of stranded wire with strands that are electrically isolated fromone another.
 19. A system as in claim 15, further comprising atransmitting antenna that transmits magnetic energy.
 20. A system as inclaim 16, wherein said parasitic antenna includes a tuning part that isadjustable to change a resonant frequency of said parasitic antenna. 21.A system as in claim 20, wherein said tuning part includes a variablecapacitance.
 22. A system as in claim 20, wherein said tuning part onlyadjusts said resonant frequency in a downward direction.
 23. A system asin claim 20, wherein said tuning part includes a portion that shortcircuits a portion of said inductive loop.
 24. A system as in claim 23,wherein said tuning part has a variable size to change an area of theinductive loop that it short circuits.
 25. A system as in claim 24,wherein said part is triangular in its outer shape.
 26. A system as inclaim 22, wherein said variable capacitance is a switched capacitance.27. A system, comprising: a parasitic antenna, formed of an inductiveloop in series with a capacitance, said inductive loop is formed of amaterial that increases an effective cross sectional area of a wire usedfor the parasitic antenna without increasing an actual cross sectionalarea of the wire, an LC value of the inductive loop and capacitancedefining a resonant frequency at a specified frequency, to receive andrepeat said specified frequency of magnetically-generated wireless powerin an area of said parasitic antenna.
 28. A system as in claim 27,wherein said inductive loop is formed of stranded wire with multiplestrands of wire that are electrically isolated from one another.
 29. Asystem as in claim 28, wherein said stranded wire is Litz wire.
 30. Asystem as in claim 27, further comprising a transmitting antenna thattransmits magnetic energy at said specified frequency.
 31. A system asin claim 27, wherein said parasitic antenna includes a tuning part thatis adjustable to change a resonant frequency of said parasitic antenna.32. A system as in claim 31, wherein said tuning part includes avariable capacitance.
 33. A system as in claim 31, wherein said tuningpart only adjusts said resonant frequency in a downward direction.
 34. Asystem as in claim 31, wherein said tuning part includes a portion thatshort circuits a portion of said inductive loop.
 35. A system as inclaim 34, wherein said tuning part has a variable size to change an areaof the inductive loop that it short circuits.
 36. A system as in claim32, wherein said variable capacitance is a switched capacitance.
 37. Asystem, comprising: a parasitic antenna, formed of an inductive loop inseries with a capacitance, an LC value of the inductive loop andcapacitance tuned to a resonant frequency at a specified frequency, toreceive and repeat said specified frequency of magnetically-generatedwireless power in an area of said parasitic antenna, said parasiticantenna including a tuning part that is adjustable to change a resonantfrequency of said parasitic antenna by short circuiting across a portionof said inductive loop.
 38. A system as in claim 37, wherein saidinductive loop is formed of a material that increases the effectivecross sectional area of a wire used for the antenna without increasingan actual cross sectional area of the wire.
 39. A system as in claim 37,further comprising a transmitting antenna which transmits magnetic powerat said specified frequency.
 40. A system as in claim 37, wherein saidpart has a variable size to change an area of the inductive loop that itshort circuits.
 41. A system as in claim 40, wherein said part istriangular.
 42. A system, comprising: a wireless power transmitter,including a magnetic field generator, that generates a magnetic field ata specified frequency, and a transmitting antenna that transmitswireless power by producing a magnetic field that has said specifiedfrequency, said transmitting antenna having an inductance, and having acapacitance, forming an LC value that is substantially resonant withsaid specified frequency, said inductance formed by an antenna loop thatextends around a loop, and the area forming the loop has at least twodifferent planar sections, with a first of the planar sections beingabove the second planar section.
 43. A system as in claim 42, furthercomprising a parasitic antenna, smaller than said loop of saidtransmitting antenna, and repeating said wireless power in an area. 44.A system as in claim 42, wherein said antenna has a first area in afirst plane, and a second area in a second plane that is horizontallyabove said first plane.
 45. A system as in claim 44, further comprisinga third portion which extends between said first and second planes. 46.A method, comprising: producing wireless power from a first antenna thatforms a first part of a magnetic resonator and which produces wirelesspower as a magnetic field; using a parasitic antenna, within a range ofsaid first antenna, to repeat said wireless power; and receiving saidmagnetic power that has been repeated by said parasitic antennawirelessly into a portable device and using said power to power saiddevice.
 47. A method as in claim 46, wherein said first antenna has alarger outer size than said second antenna.
 48. A method as in claim 46,further comprising using a material that increases an effective crosssectional area of a wire used for the antenna without increasing anactual cross sectional area of the wire.
 49. A method as in claim 46,wherein said producing uses a transmitting antenna that surrounds aperimeter of a room.
 50. A method as in claim 49, wherein saidtransmitting antenna is at different height levels in the room.
 51. Amethod as in claim 46, further comprising tuning a resonant frequency ofsaid parasitic antenna.
 52. A method as in claim 51, wherein said tuningcomprises changing a value of a variable capacitance.
 53. A method as inclaim 51, wherein said tuning comprises short circuiting a portion ofsaid inductive loop.